There is known an actuator in which a bar-like driving member is asymmetrically vibrated in its shaft direction by asymmetric expansion/contraction of a piezoelectric element and whereby a moving member friction-engaged to the driving member is slidingly moved in a single direction. Since the expansion/contraction characteristics of the piezoelectric element depend on the ambient temperature, there is a problem that the driving speed of the actuator is varied depending on the temperature change.
Patent document 1 discloses that with an ultrasonic motor using a piezoelectric element, the driving is performed at a frequency selected so as to maximize the driving speed at the ambient temperature when driving. There is a problem that the driving speed is typically increased with temperature. In addition, with vibration actuators, the frequency-dependent driving speed characteristics do not conform to the frequency-dependent driving force characteristics. As a result, there is a problem that the driving force depends on the chive frequency appropriate to the ambient temperature.